1. Field of the Invention
Present invention relates to an apparatus for magnetic tape recording/reproducing, such as a digital audio tape recorder (hereinafter referred to as DAT), wherein plural systems of data, for example, video data and audio data, are compositely recorded so that the recorded data can be reproduced separately for individual systems, and to a method for such tape recording/reproducing.
2. Description of the Prior Art
FIG. 1 is an illustration schematically showing general aspect of a recording format in which two systems of data, i.e., video data and audio data, are recorded on a magnetic tape in recording areas partitioned separately for individual systems of data, and the locus of an operation for retrieving desired data from the magnetic tape. FIG. 1 (1) shows the order of arrangement of main data, i.e., video data and audio data on the magnetic tape; FIG. 1 (2) shows the format of first identification data ID1 specifying the order of arrangement of tracks on the magnetic tape, that is, serial numbers of the tracks; FIG. 1 (3) shows the format of second identification data ID2 for identifying record areas for video data and record areas for audio data; FIG. 1 (4) shows the locus of an operation for retrieving the video data on the magnetic tape from the end of tape marker (hereinafter referred to as EOT) and toward the beginning of tape marker (hereinafter referred to as BOT); and FIG. 1 (5) shows the locus of an operation for retrieving same video data from the EOT side toward the BOT side.
In the prior art apparatus, as FIG. 1 (1) shows, video data for one screen image are recorded as one unit of video data in a main data record area having a predetermined m number of successive tracks, and audio data corresponding to the video data for one screen image are recorded in a main data record area having a predetermined n number of successive tracks continued from the first mentioned tracks; and the one unit of video data and the corresponding one unit of audio data constitute one unit of record data.
In sub-code record areas of individual tracks on the magnetic tape are recorded, in terms of serial number, first identification data ID1 according to the order of track arrangement as shown in FIG. 1 (2), and second identification data ID2 according to the order of arrangement of video data and audio data of each unit as shown in FIG. 1 (3). These identification data ID1, ID2 are utilized as an absolute time index in the case of reproducing operation and/or as a so-called "head out (beginning position search)" index in the case of screen retrieval.
When, for example, second record unit of video data on the magnetic tape is to be retrieved from the EOT side toward the BOT side, as FIG. 1 (4) shows, high speed retrieval operation is first carried out toward the record position of the video data to be searched, and when point A or the beginning position of the video data to be searched is passed, the operation is switched over to a reproducing mode operation for retrieval toward the EOT side. Once the beginning position A is passed in this retrieval operation, the retrieval operation returns to the position reached just prior to the passage of the beginning position A and from thence run is made again toward the EOT side for access to the beginning position A.
When same video data are to be retrieved from the BOT side toward the EOT side, as FIG. 1 (5) shows, high speed retrieval operation is first carried out toward the record position of the video data to be searched, and when the record position of audio data located just prior to the video data to be searched, the operation is switched over to a reproducing mode operation for retrieval toward the EOT side. Once the beginning position A is passed in this retrieval operation, the retrieval operation returns to the position reached just prior to the passage of the beginning position A and from thence run is made again toward the EOT side for access to the beginning position A.
FIG. 2 is a flow chart showing the manner of retrieval operation. The retrieval operation is explained in further detail below with reference to the flow chart.
When retrieval is started toward BOT, at step n2 next to starting step n1, high speed retrieving operation toward BOT is carried out. At next step n3, it is determined whether or not the record area whose second identification data ID2 is "2", that is, a record area of audio data just prior to that of the video data to be searched has been reached. Retrieval in same direction is continued thereafter and until that decision has been made. When the record area whose second identification data ID2 is "2" has been reached, operation, proceeds to next step n4. By this point of time, the beginning position A of the target area has been passed. At step n4, therefore, retrieval in reproducing operation mode is made toward EOT.
Then, at step n5, it is determined whether or not the record area whose identification data ID2 is "3" has been reached, that is, whether or not the record area of the target video data has been reached. Retrieval in same direction is continued thereafter and until that decision has been made. After the record area whose second identification data ID2 is "3" has been reached, and at next step n6, the first identification data ID1 which is read when that record area is reached, that is, index number (m+n+1) for the beginning track of the record area of the target video data is stored in place.
By this time, the beginning position A to be searched has been passed. At step n7, therefore, the operation returns to a position reached just prior to the beginning position A being passed, and retrieval in reproducing operation mode is repeated toward EOT. Nextly, at step n8, it is determined whether or not the beginning position A corresponding to the previously stored identification data ID1=m+n+1 has been reached. When this decision has been made, that is, the beginning position A of the video data to be searched has been retrieved, operation proceeds to next step n9 at which, for example, recording of new video data in the record area of the target video data is executed. Upon completion of that operation, the operation proceeds to next step n10 at which all operation is ended.
When retrieval is started toward EOT, at step n12 next to starting step n11, high speed retrieving operation toward EOT is carried out. At next step n13, it is determined whether or not the record area whose second identification data ID2 is "2", that is, a record area of audio data just prior to that of the video data to be searched has been reached. Thereafter and until this decision has been made, retrieving operation in same direction is continued. When the record area whose second identification data ID2 is "2" is reached, operation proceeds to next step n4. Subsequent steps of operation are same as those already explained.
In the above described prior art DAT, when video data or audio data are to be retrieved, in order to locate the beginning position of the data, that is, the number (m+n+1) of identification data ID1 of the beginning position, or boundary number for record units, as in the above described example, it is necessary to carry out a high speed retrieval operation first and then a retrieval operation in reproducing operation mode. Further, when the target beginning position A is thus recognized, the beginning position A has already been passed and, therefore, it is again necessary to carry out operation for access to the target beginning position A. This involves some wastefull movement and considerable loss of time.